Measuring Parallelograms

Transcription

1 4 Measuring Parallelograms In this unit, you have developed ways to find the area and perimeter of rectangles and of triangles. In this investigation you will develop ways to find the area and perimeter of parallelograms. When you work with rectangles, you use measurements like length and width. For triangles, you use the side lengths, the base, and the height. Like triangles, parallelograms are often described by measures of side length, base, and height. 4.1 Finding Measures of Parallelograms As you work with parallelograms, remember what you know about triangles and look for ways to relate these two figures. Investigation 4 Measuring Parallelograms 53

2 Getting Ready for Problem 4.1 Here are three parallelograms with the base and height of two parallelograms marked. What do you think the base and the height of a parallelogram mean? How do you mark and measure the base and height of the third figure? height height base base Problem 4.1 Finding Measures of Parallelograms Six parallelograms labeled A F are drawn on the centimeter grid on the next page. A. 1. Find the perimeter of each parallelogram. 2. Describe a strategy for finding the perimeter of a parallelogram. B. 1. Find the area of each parallelogram. 2. Describe the strategies you used to find the areas. 54 Covering and Surrounding

3 A B C D E F Investigation 4 Measuring Parallelograms 55

4 4.2 Parallelograms From Triangles In this problem, you will consider how the area of a parallelogram relates to its base and height. You will also consider how the area of a parallelogram relates to the area of a triangle with the same base and height. Problem 4.2 Parallelograms From Triangles At the right is parallelogram F from Problem 4.1. Trace two copies of this parallelogram. A. 1. Find two ways to position parallelogram F on a centimeter grid. 2. Record the base and height for each position you find. 3. How does the area of the parallelogram relate to the base and height in each position? B. 1. Look at parallelograms A F from Problem 4.1 again. Make a table recording the area, base, and height of each parallelogram. 2. Draw one diagonal in each parallelogram as shown below. Add columns to your table recording the area, base, and height of each triangle. F diagonal A 3. Look for patterns in your table that show how the area of each parallelogram and the area of its triangles are related. 4. How are the bases and heights of each parallelogram and the triangles made by a diagonal related? C. 1. Write a rule for finding the area of a parallelogram. Use b to represent the base and h to represent the height. 56 Covering and Surrounding

5 2. Use your rule to find the area of this parallelogram. Make any measurements you need in centimeters. 4.3 Designing Parallelograms Under Constraints Now you can draw parallelograms that meet given conditions. Sometimes you will be able to draw more than one parallelogram that satisfies the constraints given. Problem 4.3 Designing Parallelograms Under Constraints For each description, draw two figures that are not congruent (same shape, same size) to each other. If you can t draw a second figure, explain why. Make your drawings on centimeter grid paper. A. The rectangles each have an area of 18 square centimeters. If you can draw two different rectangles, do they have the same perimeter? B. The rectangles are each 3 centimeters by 8 centimeters. If you can draw two different rectangles, do they have the same area? C. The parallelograms each have a base of 7 centimeters and a height of 4 centimeters. If you can draw two different parallelograms, do they have the same area? D. The parallelograms each have all 6-centimeter side lengths. If you can draw two different parallelograms, do they have the same area? E. The parallelograms each have an area of 30 square centimeters. If you can draw two different parallelograms, do they have the same perimeter? Investigation 4 Measuring Parallelograms 57

6 4.4 Parks, Hotels, and Quilts Now that you know how to find the area of rectangles, triangles, and parallelograms, here are some problems to test your skills. Problem 4.4 Finding Areas and Perimeters A. The Luis Park District set aside a rectangular section of land to make a park. After talking with students, the park district decides to make an area for skateboarding, an area with playground equipment, and an area with a basketball court, as shown. skateboarding playground basketball 1. A fence surrounds the skateboarding area that takes up of the 3 2 length and of the width of the park. What fraction of 3 the area of the park does the skateboarding area occupy? 2. The basketball court is 35 feet by 60 feet. Use this information and what you know about the skateboarding area to find the area and the perimeter of the playground area. B. The Luxor Hotel in Las Vegas is built in the shape of a pyramid. When you look at the pyramid from the outside, each face (side) of the pyramid is a glass equilateral triangle Each face is an equilateral triangle with a base that is 646 feet and 9 a height that is approximately 559 feet. Sketch a face of the 20 pyramid. Label the base and height. 58 Covering and Surrounding

7 2. Estimate the area of the glass used to cover one triangular face. 3. If lights are strung along the three edges of one triangular face, how many feet of lights are needed? C. Quilters use shapes such as triangles, squares, rectangles, and parallelograms when designing quilts. This is a pattern of a 10 inch-by-10 inch quilt square on inch grid paper. 1. Each parallelogram in the quilt is made from how many square inches of fabric? 2. How many square inches of fabric are used to make the small red squares in the quilt square? 3. The squares and the parallelograms will be sewn onto white fabric. How many square inches of the white fabric will be visible? 1 inch Investigation 4 Measuring Parallelograms 59